LedgerIframeBridge.destroy does not remove the iframe from document

[mikesposito]

The LedgerIframeBridge.destroy method does not destroy/remove the iframe from the document: when calling destroy and then init again, the document will have two Ledger iframes, which could lead to unexpected behavior. Because of this, the default behaviour of setOptions is duplicating the current iframe.

We should remove the current iframe from the document when destroy is called.